Liquid crystal display device

ABSTRACT

In a liquid crystal display device, a common electrode is formed on an organic passivation film, an interlayer insulating film is formed on the common electrode, a pixel electrode with a slit is formed on the interlayer insulating film, and a through hole is formed in the organic passivation film and the interlayer insulating film, so that the pixel electrode is connected to a source electrode of a TFT through the through hole. Further, the taper angle around the upper base of the through hole is smaller than the taper angle around the lower base. Thus, the alignment film material can easily flow into the through hole when the diameter of the through hole is reduced to connect the pixel and source electrodes, preventing display defects such as uneven brightness due to the absence of the alignment film or due to the alignment film irregularity around the through hole.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/401,795 filed on Jan. 9, 2017, which, in turn, is a continuation ofU.S. patent application Ser. No. 15/212,873 (now U.S. Pat. No.9,575,385) filed on Jul. 18, 2016, which, in turn, is a continuation ofU.S. patent application Ser. No. 14/978,671 (now U.S. Pat. No.9,417,496) filed on Dec. 22, 2015, which, in turn, is a continuation ofU.S. patent application Ser. No. 14/527,841 (now U.S. Pat. No.9,250,491) filed on Oct. 30, 2014. Further, this application claimspriority from Japanese Patent Application No. 2013-226910 filed on Oct.31, 2013, the contents of which are hereby incorporated by referenceinto this application.

BACKGROUND

The present invention relates to a display device, and moreparticularly, to a liquid crystal display device with a minor reductionin transmittance and a small amount of pixel defects even in a highdefinition screen.

A display device includes a TFT substrate in which pixels each having apixel electrode, a thin film transistor (TFT), and the like are arrangedin a matrix form. Further, a counter substrate is disposed opposite theTFT substrate, in which color filters and the like are formed atlocations corresponding to the pixel electrodes of the TFT substrate. Aliquid crystal is interposed between the TFT substrate and the countersubstrate. Then, an image is formed by controlling the transmittance oflight through each pixel by the liquid crystal molecules.

Liquid crystal display devices are flat and lightweight and have beenapplied in various fields. Small liquid crystal display devices arewidely used in mobile phones, digital still cameras (DSC), or otherportable devices. The viewing angle property is a problem for the liquidcrystal display device. The viewing angle property is a phenomenon thatthe brightness changes or the chromaticity changes between when thescreen is viewed from the front, and when it is viewed in an obliquedirection. The viewing angle property is excellent in the In PlaneSwitching (IPS) mode for driving liquid crystal molecules by an electricfield in the horizontal direction.

Among various types in the IPS mode, for example, there is a mode inwhich a common electrode is formed in a matted manner and a comb-shapedpixel electrode is provided on the common electrode with an insulatingfilm interposed therebetween, to rotate liquid crystal molecules by theelectric field generated between the pixel electrode and the commonelectrode. This type of mode can increase the transmittance and is nowmainstream. The common electrode and the interlayer insulating film areformed on an organic passivation film that also functions as aflattening film.

Meanwhile in the liquid crystal display device, when the size of thepixel is reduced for a high definition screen, the ratio of the diameterof a through hole for connecting the pixel electrode and the sourceelectrode of the TFT is increased.

In the IPS mode liquid crystal display device described above, when theratio of the through hole to the pixel is increased, the bondingstrength between an organic passivation film and an interlayerinsulating film formed on the organic passivation film is reduced,resulting in a problem that the interlayer insulating film is removed.Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-59314)describes a configuration in which the interlayer insulating film isformed only on the organic passivation film and not within the throughhole, in order to reduce the stress on the interlayer film to preventthe interlayer film from removing.

The pixel becomes smaller as the screen is high definition. Along withthis, in order to reduce the diameter of the through hole, it isnecessary to increase the taper angle of the wall part of the throughhole (hereinafter also referred to as the taper angle). Meanwhile, thealignment film is used for the initial alignment of the liquid crystalmolecules. The alignment film material is initially liquid and isapplied by flexographic or inkjet printing, or other printing processes.

When the taper angle of the through hole is increased, there is aphenomenon that the applied alignment film material does not enter thethrough hole due to the surface tension. In this case, display defectsoccur around the through hole, such as light leakage due to the poorinitial alignment of the liquid crystal molecules, and uneven brightnessdue to the irregularity of the film thickness. Patent Document 2(Japanese Patent Application Laid-Open No. 2007-322563) describes aconfiguration in which the alignment film can easily flow into thethrough hole by changing the height around the upper side of the throughhole.

SUMMARY

In recent years, there has been a demand for a high definition screensuch as Video Graphics Array (VGA, 640×480 dots) also in small liquidcrystal display devises. Here, a dot is a set of three pixels of red,green, and blue, which is equal to 1920×480 in the number of pixels. VGAcan be enabled on a 3-inch screen when the short diameter of the pixelis a very small value such as 32 μm.

In order to maintain a predetermined transmittance even if the pixelbecomes smaller, it is necessary to provide a TFT, a through hole, andthe like, in a small area to increase the ratio of the pixel electrodeto the pixel area as much as possible. When the area occupied by thethrough hole is reduced, the taper angle of the through hole increases.As a result, the alignment film material does not easily flow into thethrough hole, resulting in display defects such as light leakage due tothe poor initial alignment of the liquid crystal molecules, as well asuneven brightness due to the irregularity of the film thickness.

Like the configuration described in Patent Document 2, when a heightdifference is provided around the upper part of the through hole, aso-called organic passivation film may not be used. The organicpassivation film is thick with a film thickness of 2 to 4 μm, so thatthe surface is flat and it is difficult to make a height differencearound the through hole.

On the other hand, it is necessary to use the organic passivation filmdue to requirements, such as a uniform layer thickness of the liquidcrystal layer, depending on the type of the liquid crystal displaydevice. Further, the problem of increasing the area occupied by thethrough hole becomes more significant when the through hole is formed inthe organic passivation film, because the organic passivation film isthick with a film thickness of 2 to 4 μm.

FIG. 10 is a cross-sectional view of the problem described above in anIPS mode liquid crystal display device. In FIG. 10, a gate insulatingfilm 101 is formed on a TFT substrate 100, and a source electrode 102from a TFT, not shown, is formed on the gate insulating film 101.Further, an organic passivation film 103 is formed on the sourceelectrode 102 and the gate insulating film 101. Then, a common electrode104 is formed on the organic passivation film 103. Then, an interlayerinsulating film 105 is formed so as to cover the common electrode 104,and a pixel electrode 106 with a slit 1061 is formed on the interlayerinsulating film 105.

The pixel electrode 106 is connected to the source electrode 102 througha through hole 108 formed in the organic passivation film 103 and theinterlayer insulating film 105. When the screen is high definition andthe area of the pixel becomes smaller, it is necessary to reduce thearea occupied by the through hole by increasing the taper angle α0 ofthe through hole 108, in order to maintain the transmittance of thepixel.

However, as shown in FIG. 10, if the taper angle α0 of the through hole108 is large, the alignment film material, which is initially liquid,does not easily flow into the through hole from an upper base 1081 ofthe through hole 108. Thus, there is a problem that the alignment filmis not formed within the through hole. Further, there is also a problemthat the thickness of the alignment film 107 increases around thethrough hole, and the irregularity of the film thickness occurs in thealignment film 107. As a result, display defects occur in the throughhole 108 and in the vicinity thereof, such as light leakage due to thepoor initial alignment of the liquid crystal molecules as well as unevenbrightness due to the irregularity of the film thickness.

An object of the present invention is to achieve a liquid crystaldisplay device using an organic passivation film in a TFT substrate, inwhich the alignment film material can easily enter the through hole,even if the area occupied by the through hole is limited when the areaof the pixel is reduced for a high definition screen.

The present invention is made to overcome the above problems andspecific solutions are as follows.

(1) There is provided a liquid crystal display device including: a TFTsubstrate including a pixel in which a common electrode is formed on anorganic passivation film, an interlayer insulating film is formed so asto cover the common electrode, a pixel electrode with a slit is formedon the interlayer insulating film, and a source electrode of a TFT iselectrically connected to the pixel electrode through a through holethat is formed in the organic passivation film and the interlayerinsulating film; and a counter substrate including a color filter at alocation corresponding to the pixel, in which a black matrix is formedbetween each of the color filters. Further, a liquid crystal isinterposed between the TFT substrate and the counter substrate. Thethrough hole is formed in the organic passivation film in such a waythat the cross section on the side near the counter substrate is theupper base, and the cross section on the side of the source electrode isthe lower base. The diameter of the upper base is greater than thediameter of the lower base. The taper angle on the side near the upperbase of the through hole formed in the organic passivation film issmaller than the taper angle on the side near the lower base.

(2) In the liquid crystal display device described in (1), if D is thedepth of the through hole formed in the organic passivation film, thetaper angle at a distance of D/6 from the upper base is smaller than thetaper angle at a distance of D/3 from the upper base.

(3) In the liquid crystal display device described in (1), if D is thedepth of the through hole formed in the organic passivation film, thetaper angle at a distance of D/3 from the upper base is smaller than thetaper angle at a distance of 2D/3 from the upper base.

(4) There is provided a liquid crystal display device including: a TFTsubstrate including a pixel in which a pixel electrode is formed on anorganic passivation film, an interlayer insulation film is formed so asto cover the pixel electrode, a common electrode with a slit is formedon the interlayer insulating film, and a source electrode of a TFT iselectrically connected to the pixel electrode through a through holethat is formed in the organic passivation film and the interlayerinsulating film: and a counter substrate including a color filter at alocation corresponding to the pixel, in which a black matrix is formedbetween each of the color filters. Further, a liquid crystal isinterposed between the TFT substrate and the counter substrate. Thethrough hole is formed in the organic passivation film in such a waythat the cross section on the side near the counter substrate is theupper base, and the cross section on the side of the source electrode isthe lower base. The diameter of the upper base is greater than thediameter of the lower base. The taper angle on the side near the upperbase of the through hole formed in the organic passivation film, issmaller than the taper angle on the side near the lower base.

According to the present invention, in a liquid crystal display deviceusing an organic passivation film in a TFT substrate with the pixel areareduced for a high definition screen, it is possible to stably form aliquid alignment film material within a through hole even if thediameter of the through hole is reduced. Thus, it is possible to preventdisplay defects such as uneven brightness due to the absence of thealignment film within the through hole, or due to the irregularity ofthe film thickness of the alignment film around the through hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a pixel of a liquid crystal display device towhich the present invention is applied;

FIGS. 2A, 2B, and 2C are examples of the plane shape of a through hole;

FIG. 3 is a cross-sectional view of a portion of the through hole in apixel of a liquid crystal display device according to a firstembodiment;

FIG. 4 is a cross-sectional view of the through hole formed in anorganic passivation film according to the first embodiment;

FIG. 5 is a cross-sectional view of the through hole formed in theorganic passivation film with a smooth wall surface according to thefirst embodiment;

FIG. 6 is a detailed cross-sectional view of FIG. 5;

FIG. 7 is a cross-sectional view of the through hole in which threetypes of taper angles are formed according to the first embodiment;

FIG. 8 is a cross-sectional view of an example of the through hole inwhich a step is formed between a first taper angle and a second taperangle according to the first embodiment;

FIG. 9 is an example of a liquid crystal display device according to asecond embodiment, in which the inside of the through hole is also usedfor image formation; and

FIG. 10 is a cross-sectional view around the through hole in a liquidcrystal display device of a conventional example.

DETAILED DESCRIPTION

Hereinafter, the details of the present invention will be described withreference to the preferred embodiments.

First Embodiment

FIG. 1 is a plan view of a pixel in a TFT substrate 100 of a liquidcrystal display device to which the present invention is applied. FIG. 1is an example of an IPS mode liquid crystal display device. In FIG. 1,scanning lines 10 extend in the horizontal direction and are arranged inthe vertical direction at a predetermined pitch PY. Further, videosignal lines 20 extend in the vertical direction and are arranged in thehorizontal direction at a predetermined pitch PX. An area surrounded bythe scanning lines 10 and the video signal lines 20 is a pixel.

In FIG. 1, a gate electrode 11 is branched from the scanning line 10,and a semiconductor layer 30 is formed on the gate electrode 11. Then, adrain electrode 21 branched from the video signal line 20 is formed onthe semiconductor layer 30. Further, a source electrode 102 is formed onthe semiconductor layer 30. The source electrode 102 extends in thedirection of a pixel electrode 106. The width of the source electrode102 is increased in the area overlapping the pixel electrode 106, whichis below the through hole 108. The source electrode 102 also functionsas a light shielding film for preventing light leakage in the throughhole 108.

In FIG. 1, the pixel electrode 106 with a slit 1061 is formed in arectangular shape. An interlayer insulating film, not shown, is formedbelow the pixel electrode 106. Then, a planar common electrode, notshown, is formed below the interlayer insulating film. Then, electriclines of force from the pixel electrode 106 are formed toward the commonelectrode (not shown) through the portion of the slit 1061.

In FIG. 1, the pixel electrode 106 is connected to the source electrode102 through the through hole 108. The through hole 108 is formed in theorganic passivation film, not shown, whose film thickness is thick.Thus, the through hole 108 has a taper including un upper base 1081 witha large diameter as well as a lower base 1082 with a small diameter. Thesource electrode 102 is slightly greater than the through hole 108. Thesource electrode 102 also functions as a light shielding film for thethrough hole 108.

In FIG. 1, the pixel has a rectangular shape, in which the smallerdiameter of the pixel is represented by PX. Further, in FIG. 1, thethrough hole 108 has substantially a square shape, in which thehorizontal diameter of the through hole 108 is represented by TX. FIGS.2A, 2B, and 2C are other examples of the plane shape of the through hole108. FIG. 2A shows the through hole 108 with a rectangular shape, inwhich TX is the short diameter. FIG. 2B shows the through hole 108 witha circular shape. In this case, the diameter is constant and representedby TX. FIG. 2C shows the through hole 108 with an oval shape, in whichTX is the short diameter.

In the high definition screen, the pixel area is reduced and the areaoccupied by the through hole is increased relative to the pixel area.More specifically, the present invention is particularly effective whenthe short diameter TX of the through hole is one fourth or more of theshort diameter PX of the pixel. In order to maintain the transmittanceof the pixel, the area of the through hole is reduced as the pixel areabecomes small. In this case, if the taper of the through hole isincreased, the alignment film material does not easily enter the throughhole.

FIG. 3 is a cross-sectional view of the liquid crystal display device ofa portion including the through hole 108 according to the presentinvention, which is designed to address the above problem. In FIG. 3,the gate insulating film 101 is formed on the TFT substrate 100, thesource electrode 102 is formed on the gate insulating film 101, and theorganic passivation film 103 is formed on the source electrode 102. Thisis the same as in the conventional example. The feature of the presentinvention is the shape of the through hole 108 in the organicpassivation film 103.

In FIG. 3, the through hole 108 formed in the organic passivation film103 has a folding point, in which the taper angle α2 on the upper sideis smaller than the taper angle α1 on the lower side. However, thediameter of the upper base of the organic passivation film 103 is thesame as the diameter of the conventional example. Thus, the ratio ofarea of the through hole to the pixel is the same as that in theconventional example.

The common electrode 104 is formed of indium tin oxide (ITO) in a planarshape on the organic passivation film 103. The common electrode 104 iscovered by the interlayer insulating film 105. The interlayer insulatingfilm 105 is formed along the organic passivation film 103, in which thethrough hole 108 is formed. The pixel electrode 106 is formed on theinterlayer insulating film 105. The pixel electrode 106 is connected tothe source electrode 102 in the through hole 108, so that a video signalis supplied to the pixel electrode 106 through the TFT.

The pixel electrode 106 has the slit 1061. Electric lines of force fromthe pixel electrode 106 extend down to the common electrode 104 throughthe slit 1061. Liquid crystal molecules 301 are driven by the electriclines of force to control the transmittance of light in the pixel. Thealignment film 107 is formed on the pixel electrode 106. The taper angleon the upper side of the through hole 108 is small, so that thealignment film material, which is initially liquid, can easily enter thethrough hole 108. Thus, in the present invention, the problem that thealignment film material does not enter the through hole 108 as shown inFIG. 10 is solved.

In FIG. 3, the counter substrate 200 is disposed opposite the TFTsubstrate 100, and the liquid crystal layer 300 is interposed betweenthe TFT substrate 100 and the counter substrate 200. In the countersubstrate 200, a color filter is formed at a location corresponding tothe pixel electrode 106. However, a black matrix 202 is formed at alocation corresponding to the through hole 108. The portion of thethrough hole 108 does not contribute to image formation, so that thelight is blocked by the black matrix 202 in order to increase thecontrast. An overcoat film 203 is formed so as to cover the color filter201 and the black matrix 202. Then, the alignment film 107 is formed soas to cover the overcoat film 203.

In FIG. 3, the film thickness of the organic passivation film 103 in theTFT substrate 100 is greater than the film thickness of the other films.Thus, the shape of the through hole 108 is determined by the shape ofthe through hole 108 of the organic passivation film 103. FIG. 4 is across-sectional view of the shape of the part of the through hole 108 ofthe organic passivation film 103. The film thickness D of the organicpassivation film 103 is about 2 to 4 μm, which is very thick compared tothe other films.

Photosensitive resin is used for the organic passivation film 103, sothat there is no need to use a resist for patterning. Examples of thephotosensitive resin are an acrylic resin, a silicon resin, and thelike. Further, a positive type photosensitive resin is used in which thetaper angle can be controlled by heating after development.

In FIG. 4, the taper angle α2 around the upper base of the through holeis smaller than the taper angle α1 around the lower base. This is toallow the alignment film material to easily flow into the through hole.In FIG. 4, the through hole has a folding point 1083 between the upperbase 1081 and the lower base 1082. Because of this, there is adifference between the taper angle in the upper base 1081 and the taperangle in the lower base 1082. In FIG. 4, the taper angle α2 around theupper base 1081 of the through hole is 10 degrees or more and 60 degreesor less, and more preferably, 10 degrees or more and 50 degrees or less.

In FIG. 4, if D is the film thickness of the organic passivation film103, the taper angle α2 at a distance of D/3 from the upper surface ofthe organic passivation film 103 is smaller than the taper angle α1 at adistance of 2D/3 from the upper surface of the organic passivation film103. Or more specifically, there is a part in which the taper angle at adistance of D/3 or less from the upper surface of the organicpassivation film 103, is smaller than the taper angle at a distance of2D/3 or more from the upper surface of the passivation film.

In FIG. 4, the taper angle α2 on the upper side is measured by using theC-C line as the reference. The C-C line is parallel to the A-A line,which is the line connecting the upper surfaces of the organicpassivation film 103. Further, the taper angle α1 on the lower side ismeasured by using the B-B line as the reference. The B-B line isparallel to the A-A line, which is the line connecting the uppersurfaces of the organic passivation film 103.

As described above, the taper angle on the side of the upper base 1081of the through hole 108 is made smaller than the taper angle on the sideof the lower base 1082 by providing the folding point 1083 in thethrough hole 108. This method can be performed by half exposure. Inother words, the organic passivation film 103 is formed of a positivetype photosensitive resin, so that it is possible to make a differencein the taper angle in such a way that the amount of exposure around theupper base 1081 is smaller than the amount of exposure around the lowerbase 1082.

The half exposure is performed by changing the transmittance of themask. More specifically, it is possible to control the transmittance oflight, for example, by allowing complete transmission of light aroundthe center of the through hole 108 while completely blocking light onthe outside of the through hole 108, and by forming, for example, smallslits in the part to be half exposed in the middle section of thethrough hole 108. The taper angle can be controlled by changing thedensity of the slits in the half exposed part.

In the present invention, a positive type photosensitive resin is usedfor the organic passivation film 103, so that the taper of the throughhole 108 can be smoothed by heating after development. FIG. 5 is anexample in which the taper is smoothed by heating after development, inwhich a dashed line 1085 shows the shape of the through hole 108 afterheating. In this case, the folding point is not often seen clearly.

In FIG. 5, if D is the film thickness of the organic passivation film103, the angle α2 of the edge of the wall of the through hole 108located at a distance of D/3 from the upper surface of the organicpassivation film 103 with respect to the C-C line, is smaller than theangle α1 of the edge of the wall of the through hole 108 located at adistance of 2D/3 from the upper surface with respect to the B-B line. Ormore specifically, there is a part in which the taper angle of the edgeof the wall of the through hole 108 located at a distance of D/3 or lessfrom the upper surface of the organic passivation film 103 with respectto the C-C line, is smaller than the taper angle of the edge of the wallof the through hole 108 located at a distance of 2D/3 or more from theupper surface of the organic passivation film 103 with respect to theB-B line. Here, the B-B line and the C-C line are parallel to the A-Aline connecting the upper surfaces of the organic passivation film 103.

FIG. 6 is a further detailed cross-sectional view of an example in whichthe taper of the through hole is smoothed by heating after development,in which the dashed line 1085 shows the shape of the through hole afterheating. In FIG. 6, if D is the film thickness of the organicpassivation film 103, an angle α3 of the edge of the wall of the throughhole 108 located at a distance of D/6 from the upper surface of theorganic passivation film 103 with respect to the E-E line, is smallerthan the angle α2 of the edge of the wall of the through hole 108located at a distance of D/3 from the upper surface with respect to theC-C line. Or more specifically, there is a part in which the angle ofthe edge of the wall of the through hole 108 located at a distance ofD/6 or less from the upper surface of the organic passivation film 103with respect to the E-E line, is smaller than the angle of the edge ofthe wall of the through hole 108 located at a distance of D/3 or morefrom the upper surface of the organic passivation film 103 with respectto the C-C line. Here, the E-E line and the C-C line are parallel to theA-A line connecting the upper surfaces of the organic passivation film103.

Further, in FIG. 6, the relationship between the angles α2 and α1 is thesame as the relationship described in FIG. 5. Thus, in FIG. 6, the taperangles of the through hole have the relationship as follows: α1<α2<α3.In other words, in FIG. 6, the higher in the through hole 108 thesmaller the taper angle of the through hole 108. Thus, the through hole108 shown in FIG. 6 has a shape such that the liquid alignment filmmaterial can easily flow into the through hole. Further, the greater andsteeper the taper angle α1 is, the more the effective ratio of thethrough hole to the pixel area can be reduced. As a result, the effectof increasing the transmittance of the pixel can also be expected. InFIG. 6, the taper angle α1 is 60 degrees or more, and more preferably,70 degrees or more.

FIG. 7 is a cross-sectional view of the through hole 108 having astructure in which two folding points are provided in the through hole108, and three types of taper angles are formed in the through hole 108in such a way that the closer the taper angle is to the side of theupper base 1081 of the through hole 108, the smaller the degree of taperangle. The through hole 108 shown in FIG. 7 can be formed by using twotypes of half exposures with different transmittance values.

In FIG. 7, if D is the film thickness of the organic passivation film103, α3 is the taper angle at a distance of D/6 down from the uppersurface of the through hole 108, α2 is the taper angle at a distance ofD/3 down from the upper surface of the through hole 108, and α1 is thetaper angle at a distance of 2D/3 down from the upper surface of thethrough hole 108. The E-E line is used as the reference line for thetaper angle α3, the C-C line is used as the reference line for the taperangle α2, and the B-B line is used as the reference line for the taperangle α1. These reference lines are parallel to the A-A line connectingthe upper surfaces of the organic passivation film 103, respectively. InFIG. 7, the taper angle α3 around the upper base of the through hole 108is 10 degrees or more and 45 degrees or less, and more preferably, 10degrees or more and 30 degrees or less.

FIG. 7 is a cross-sectional view of the through hole 108 afterdevelopment. Since the organic passivation film 103 is positive type,the shape of the through hole 108 is smoothed by heating afterdevelopment. The two folding points 1083 disappear and a smooth curvecan be formed in such a way that the closer the taper angle is to theside of the upper base 1081 of the through hole 108, the smaller thedegree of the taper angle. Further, the greater and steeper the taperangle α1 is, the more the effective ratio of the through hole to thepixel area can be reduced. As a result, the effect of increasing thetransmittance of the pixel can also be expected. In FIG. 7, the taperangle α1 is 60 degrees or more, and more preferably, 70 degrees or more.

FIG. 8 is a cross-sectional view of another form of the through hole 108according to the present embodiment. FIG. 8 is different from FIG. 4 andother figures in that a step 1084 is formed between a first wall surfacewith the taper angle α1, and a second wall surface with the taper angleα2. Here, the taper angle α2 is the taper angle at a distance of D/3from the upper surface of the through hole 108. Further, the taper angleα1 is the taper angle at a distance of 2D/3 from the upper surface ofthe through hole 108.

In FIG. 8, the taper angle α2 is smaller than the taper angle α1. InFIG. 8, the taper angle α2 around the upper base 1081 of the throughhole 108 is 10 degrees or more and 60 degrees or less, and morepreferably, 10 degrees or more and 50 degrees or less.

The angle between the taper angle α1 and the step 1084 is large but thewidth w of the step is small, so that the alignment film material, whichis liquid, does not stay in this portion. On the other hand, the taperangle α2 of the second wall near the upper surface of the through hole108 is small, so that the alignment film material stays around the upperbase 1081 of the through hole 108, thereby preventing the phenomenonthat the alignment film material does not flow into the through hole108. Thus, even if the through hole 108 has the shape of FIG. 8, thealignment film material can still easily flow into the through hold.Further, the greater and steeper the taper angle α1 is, the more theeffective ratio of the through hole to the pixel area can be reduced. Asa result, the effect of increasing the transmittance of the pixel canalso be expected.

Second Embodiment

In the present invention, as shown in FIG. 3 or 4 in the firstembodiment, the folding points are formed in the through hole 108, andthe taper angle at the position close to the upper base of the throughhole 108 is made smaller than the taper angle at the position close tothe lower base of the through hole 108. Because of this configuration,the alignment film material can easily flow into the through hole 108,so that the alignment film 107 can be uniformly formed also within thethrough hole 108. By taking advantage of this technique, it is possibleto achieve alignment of the liquid crystal molecules 301 also within thethrough hole 108, and to increase the transmittance of the pixel.

In FIG. 9 showing the present embodiment, the organic passivation film103 is formed on the gate insulating film 101. The through hole 108 isformed in the organic passivation film 103 in such a way that the taperangle on the side near the upper base of the through hole 108 is smallerthan the taper angle on the side near the lower base of the through hole108. The common electrode 104 is formed on the organic passivation film103 to a position close to the lower base of the through hole 108.However, the common electrode 104 is not electrically connected to thesource electrode 102 formed on the gate insulating film 101.

The interlayer insulating film 105 is formed so as to cover the commonelectrode 104. Then, the pixel electrode 106 is formed on the interlayerinsulating film 105. The slit 1061 is formed in the pixel electrode 106,which extends to the through hole 108. Thus, according to theconfiguration shown in FIG. 9, it is possible to control the liquidcrystal molecules 301 even within the through hole 108. In other words,the part of the through hole 108 can also be used for image formation.As a result, the transmittance of the pixel can be increased and thebrightness of the screen can be increased.

The alignment film 107 is formed on the pixel electrode 106, in whichthe taper angle on the side near the upper base of the through hole 108is made small so that the alignment film material can easily flow intothe through hole 108. Because of this configuration, the alignment film107 can be formed uniformly also within the through hole 108. As aresult, the inner part of the through hole 108 in which the commonelectrode 104 is formed and the slit 1061 of the pixel electrode 106 isformed, can also be used for image formation.

In the existing configuration, the liquid crystal molecules 301 are notcontrolled within the through hole 108, so that the source electrode 102having the role of a light shielding film covers over the through hole108 in the lower part of the through hole 108 to prevent light leakagein the through hole 108. Further, the black matrix 202 for blockinglight formed in the counter substrate 200 also covers over the throughhole 108. Because of this configuration, the transmittance of the pixelis reduced.

As can be seen by comparing FIG. 9 in the present embodiment with FIG. 3in the first embodiment, the width SW of the source electrode forblocking light, as well as the width BW of the black matrix shown inFIG. 9 are smaller than those shown in FIG. 3. In other words, the areaof the source electrode 102 as well as the area of the black matrix 202formed in the counter substrate 200 shown in FIG. 9, are smaller thanthe area of the source electrode 102 as well as the area of the blackmatrix 202 formed in the counter substrate 200 shown in FIG. 3. Becauseof this, the transmittance of the pixel can be increased in theconfiguration of FIG. 9. In particular, when the taper angle at adistance of D/3 from the upper base of the through hole is made smallerand more moderate, and when the taper angle at a distance of 2D/3 fromthe upper base of the through hole is made steeper, the area capable ofeffective display can be provided without the influence of the thicknessof the liquid crystal layer. At the same time, the effect of increasingthe transmittance of the pixel is significant. Note that theconfiguration of the counter substrate 200 in FIG. 9 is the same as theconfiguration described in FIG. 3 except that the area of the blackmatrix 202 is small, so that the description thereof is omitted.

It is necessary to perform the alignment treatment of the alignment film107 to provide the initial alignment of the liquid crystal molecules301. In the rubbing treatment performed in the past, it is difficult torub the alignment film 107 including the concave portion. On the otherhand, there is a so-called photo-alignment treatment, which is a methodfor providing uniaxial anisotropy to the alignment film 107 by polarizedultraviolet light. The photo-alignment can emit ultraviolet light alsoto the inside of the through hole 108. Thus, it is possible to performthe alignment treatment on the alignment film within the through hole108.

In the present invention, the taper angle of the through hole 108 issmall in the part close to the upper base of the through hole 108. Thus,it is easy to form the slit 1061 of the pixel electrode 106 in this partof the through hole 108 to use it as an area for image formation.

The forgoing has described the configuration of a so-called pixelelectrode top in which the common electrode 104 is formed on the organicpassivation film 103, the interlayer insulating film 105 is formed so asto cover the common electrode 104, and the pixel electrode 106 with theslit 1061 is formed on the interlayer insulating film 105. On the otherhand, there is a configuration of a so-called common electrode top inwhich the pixel electrode 106 is formed on the organic passivation film103, the interlayer insulating film 105 is formed so as to cover thepixel electrode 106, and the common electrode 104 with a slit is formedon the interlayer insulating film 105. Also in this configuration, thepixel electrode 106 is connected to the source electrode 102 within thethrough hole 108 on which the interlayer insulating film 105 is formed,and the common electrode 104 is formed on the interlayer insulating film105 over the through hole.

The present invention can also be applied to an IPS mode liquid crystaldisplay device of such a common electrode top structure. In other words,there is the effect of allowing the liquid crustal material to easilyflow into the through hold in such a way that the taper angle on theside near the upper base of the through hole of the organic passivationfilm 103 is made smaller than the taper angle on the side near the lowerbase, which is the same as described in the first embodiment. Inaddition, there is the effect of allowing the inside of the through holeto also contribute to image formation by forming a slit in the commonelectrode 104 within the though hole, which is the same as described inthe second embodiment.

Further, TFT used as a switching element of the pixel has twostructures: the top gate structure and the bottom gate structure. Theconfiguration shown in FIG. 3 assumes a bottom gate type TFT, but thepresent invention is not limited to this example. The present inventioncan be applied to all types of TFT structures. Further, in the aboveembodiments, the description has been given by taking the IPS modeliquid crystal display device as an example. However, the presentinvention can also be applied to liquid crystal display devices of othertypes having an alignment film.

While the above has described the configuration in which the organicpassivation film is directly formed on the gate insulating film and thesource electrode, the present invention can also be applied to theconfiguration in which an inorganic passivation film of SiN and the likeis formed on the gate insulating film and the source electrode.

Further, in the configuration described above, the color filter isformed in the counter substrate. However, the present invention can alsobe applied to the configuration in which the color filter is formed onthe side of the TFT substrate. Further, in the above embodiments, it isalso possible that a colored organic passivation film is used as thecolor filter. Also in this case, the present invention can be appliedwithout problem. In other words, in these cases, the present inventioncan be applied under the assumption that the color filter corresponds tothe organic passivation film in each of the embodiments.

What is claimed is:
 1. A display device comprising: a first substrateincluding a source electrode of a switching element, an organic filmformed on the source electrode, a first electrode formed on the organicfilm, an insulating film formed on the first electrode, and a secondelectrode formed on the insulating film, wherein the second electrodehas a slit and is electrically connected to the source electrode througha through hole, and wherein the slit extends in the through hole.
 2. Thedisplay device according to claim 1, wherein the first electrode isformed in the through hole and is not connected to the source electrode.3. The display device according to claim 1, wherein a wall of thethrough hole has a smooth slope, and wherein the wall of the throughhole which at a position close to the first substrate is steeper thanthe wall of the through hole which at a distal position from the firstsubstrate.
 4. The display device according to claim 1, wherein thethrough hole has a first portion which is close to the first substrate,and a second portion which is distant from the first substrate, whereina taper angle of the first portion is greater than a taper angle of thesecond portion.
 5. The display device according to claim 4, wherein thethrough hole has a folding point which is disposed between the firstportion and the second portion.
 6. The display device according to claim4, wherein the through hole has a step which is disposed between thefirst portion and the second portion.
 7. The display device according toclaim 1, wherein the slit in the through hole does is not overlaps withthe source electrode, in a plan view.
 8. The display device according toclaim 1, wherein an edge of the source electrode is nearer to the centerof the though hole than an edge of the slit in the through hole, in aplan view.
 9. The display device according to claim 1, wherein a crosssection of the through hole has a lower base at a proximal position tothe first substrate side and an upper base at a distal position to thefirst substrate side, wherein a width of the upper base is greater thana width of the source electrode.
 10. The display device according toclaim 9, further comprising a second substrate opposing to the firstsubstrate, wherein the second substrate has a light shield film whichoverlaps with the source electrode in a plan view, and wherein a widthof the light shield film is equal to the width of the source electrode.11. The display device according to claim 1, further comprising analignment film covers the first substrate, wherein the alignment film isa photo alignment film, and wherein the alignment film is formed in thethrough hole.
 12. A display device comprising: a first substrateincluding a source electrode of a switching element, an organic filmformed on the source electrode, a first electrode formed on the organicfilm, an insulating film formed on the first electrode, and a secondelectrode formed on the insulating film, wherein the second electrodehas a slit and is electrically connected to the source electrode througha through hole, wherein the slit is extended to the through hole, andwherein the slit in the through hole does not overlap with the sourceelectrode, in a plan view.
 13. The display device according to claim 12,further comprising an alignment film covers the first substrate, whereinthe alignment film is a photo alignment film, and wherein the alignmentfilm is formed in the through hole.
 14. The display device according toclaim 12, wherein the through hole has a first portion which is close tothe first substrate, and a second portion which is distant from thefirst substrate, wherein a taper angle of the first portion is greaterthan a taper angle of the second portion.
 15. The display deviceaccording to claim 14, wherein a width of the first portion is greaterthan a width of the source electrode, in a plan view.
 16. The displaydevice according to claim 15, further comprising a second substrateopposing to the first substrate, wherein the second substrate has alight shield film which overlaps with the source electrode, and whereina width of the light shield film is equal to the width of the sourceelectrode.